Apparatus and Method for Controlling Audio-Frame Division

1. An apparatus for encoding an audio signal, comprising: an acoustic analyzer that analyzes the audio signal to calculate perceptual entropy indicating how many bits are required for quantization; a coded bit count monitor that monitors the number of coded bits produced from the audio signal and calculates the number of available bits for a current frame; a frame division number determiner that determines a division number N for dividing a frame of the audio signal into N blocks, based on a combination of the perceptual entropy and the number of available bits, such that the N blocks will have lengths suitable for suppressing sound quality degradation due to pre-echoes and bit starvation; an orthogonal transform processor that divides the frame by the determined division number and subjects each divided block of the audio signal to an orthogonal transform process, thereby obtaining orthogonal transform coefficients; and a quantizer that quantizes the orthogonal transform coefficients on a divided block basis; wherein: the frame division number determiner comprises a conversion map defining the division number with respect to the perceptual entropy and the number of available bits; the conversion map gives a larger division number for a larger perceptual entropy, so that the resulting blocks will have shorter lengths suitable for suppressing pre-echoes and consequent degradation of sound quality; and the conversion map gives a smaller division number for a smaller number of available bits, so that the resulting blocks will have longer lengths suitable for suppressing bit starvation and consequent degradation of sound quality.

2. An apparatus for encoding an audio signal, comprising: an acoustic analyzer that analyzes the audio signal to calculate perceptual entropy indicating how many bits are required for quantization; a coded bit count monitor that monitors the number of coded bits produced from the audio signal and calculates the number of available bits for a current frame; a frame division number determiner that determines a division number N for dividing a frame of the audio signal into blocks, based on a combination of the perceptual entropy and the number of available bits, such that the N blocks will have lengths suitable for suppressing sound quality degradation due to pre-echoes and bit starvation; an orthogonal transform processor calculates first orthogonal transform coefficients by performing an orthogonal transform on the entire frame in the case of N=1, calculates second orthogonal transform coefficients by dividing the frame by a maximum division number Nmax and performing an orthogonal transform on each divided block of the audio signals in the case of N=Nmax, and calculates the second orthogonal transform coefficients by dividing the frame by the maximum division number and performing an orthogonal transform thereon and combines the calculated second orthogonal transform coefficients into as many groups as the division number N in the case of 1<N<Nmax; and a quantizer that quantizes the first orthogonal transform coefficients on an entire frame basis in the case of N=1, quantizes the second orthogonal transform coefficients on a divided block basis in the case of N=Nmax, and quantizes the second orthogonal transform coefficients on an individual group basis in the case of 1<N<N max.

3. The apparatus according to claim 2 , wherein: the frame division number determiner comprises a conversion map defining the division number with respect to the perceptual entropy and the number of available bits; the conversion map gives a larger division number for a larger perceptual entropy, so that the resulting blocks will have shorter lengths suitable for suppressing pre-echoes and consequent degradation of sound quality; and the conversion map gives a smaller division number for a smaller number of available bits, so that the resulting blocks will have longer lengths suitable for suppressing bit starvation and consequent degradation of sound quality.

4. The apparatus according to claim 2 , wherein the orthogonal transform processor defines boundaries between groups in such way that a group of blocks containing or near a point where the audio signal varies will have a shorter length.

5. A method of encoding audio signals, comprising: analyzing the audio signal to calculate perceptual entropy indicating how many bits are required for quantization; monitoring the number of coded bits produced from the audio signal to calculate the number of available bits for a current frame; determining a division number N for dividing a frame of the audio signal into N blocks, based on a combination of the perceptual entropy and the number of available bits, such that the N blocks will have lengths suitable for suppressing sound quality degradation due to pre-echoes and bit starvation; dividing the frame by the determined division number and subjecting each divided block of the audio signal to an orthogonal transform process, thereby obtaining orthogonal transform coefficients; quantizing the orthogonal transform coefficients on a divided block basis; and providing a conversion map defining the division number with respect to the perceptual entropy and the number of available bits, wherein the conversion map giving a larger division number for a larger perceptual entropy, so that the resulting blocks will have shorter lengths suitable for suppressing pre-echoes and consequent degradation of sound quality, and wherein the conversion map gives a smaller division number for a smaller number of available bits, so that the resulting blocks will have longer lengths suitable for suppressing bit starvation and consequent degradation of sound quality.

6. A method of encoding audio signals, comprising: analyzing the audio signal to calculate perceptual entropy indicating how many bits are required for quantization; monitoring the number of coded bits produced from the audio signal to calculate the number of available bits for a current frame; determining a division number N for dividing a frame of the audio signal into blocks, based on a combination of the perceptual entropy and the number of available bits, such that the N blocks will have lengths suitable for suppressing sound quality degradation due to pre-echoes and bit starvation; in the case of N=1, calculating first orthogonal transform coefficients by performing an orthogonal transform on the entire frame; in the case of N being equal to a maximum division number Nmax, calculating second orthogonal transform coefficients by dividing the frame by the maximum division number and performing an orthogonal transform on each divided block of the audio signals; in the case of 1<N<Nmax, calculating the second orthogonal transform coefficients by dividing the frame by the maximum division number and performing an orthogonal transform thereon and combines the calculated second orthogonal transform coefficients into as many groups as the division number N; in the case of N=1, quantizing the first orthogonal transform coefficients on an entire frame basis; in the case of N=Nmax, quantizing the second orthogonal transform coefficients on a divided block basis; in the case of 1<N<Nmax, quantizing the second orthogonal transform coefficients on an individual group basis.

7. The method according to claim 6 , further comprising providing a conversion map defining the division number with respect to the perceptual entropy and the number of available bits, wherein the conversion map giving a larger division number for a larger perceptual entropy, so that the resulting blocks will have shorter lengths suitable for suppressing pre-echoes and consequent degradation of sound quality, and wherein the conversion map gives a smaller division number for a smaller number of available bits, so that the resulting blocks will have longer lengths suitable for suppressing bit starvation and consequent degradation of sound quality.

8. The method according to claim 6 , wherein further comprising defining boundaries between groups in such way that a group of blocks containing or near a point where the audio signal varies will have a shorter length.